The Idea Factory - Witness the Magic

Teenaged girl wants to try out for a singing competition, but the mother refuses to let her. She does it anyway, in disguise so she doesn't get in trouble. She's an immediate success, beyond the competition show. When she goes home, the mother is furious, but there's a man there that tells her they're in WitSec. The mother used to be a big star, but then she witnessed a murder. They agree to let her continue, as long as she keeps up the disguise.